Studies will be undertaken to develop modes of gene delivery to experimental neural tumors for therapeutic intervention. Neoplastic lesions associated with tuberous sclerosis (TSC) including subependymal glial nodules, giant cell astrocytomas and cortical hamartomas, are believed to represent the consequences of loss of tumor suppressor genes on growth of astrocytes, neuroprogenitor cells and mesenchymal elements. Tumor models in the TSC2 heterozygous and conditional knock-out mice have been chosen as they are genotypically similar to mutations seen in patient cells and derive spontaneously from endogenous cells. They include liver hemangiomas, renal cell carcinomas, cortical hamartomas, and potentially subependymal glial nodules. Gene delivery to these tumor cells will be explored using three types of hybrid amplicon vectors derived from herpes simplex virus type 1 (HSV): one bearing a tetracycline (tet)-regulatable transgene cassette; one bearing elements of adeno-associated virus (AAV) to promote chromosomal integration; and one with both Epstein Barr virus (EBV), elements to promote episomal retention, and retrovirus vector elements (RV), to convert amplicon-infected cells into retrovirus producer cells. Vectors will be delivered through the intra-vascular route, either directly or via endothelial carrier cells to vascularized tumor foci; by intrathecal injection for brain lesions; and by direct intratumoral injection to large tumor masses. The efficiency and longevity of gene delivery to tumors in vivo will be established using reporter genes. Effective delivery modalities will incorporate therapeutic transgenes for anti-angiogenic and apoptosis factors, and consequences to tumor growth and pathology will be evaluated. In parallel, we will incorporate additional elements into these vector systems to increase the fidelity of regulatable transgene expression and to facilitate gene delivery to slowly growing tumors, typically seen in patients. This will include, in the first case, use of a tetracycline-silencer element and elimination of the VP16 transactivating protein from virions to achieve a "full off? state in the absence of drug, and, in the second case, replacement of RV elements in the HSV/EBV vector with components of lentivirus (LV) vectors, which are able to integrate transgenes into both dividing and non-dividing cells. TSC2 +/-transgenic and TSC1 conditional knock-out animals will be provided by Dr. Kwiatkowski (Project 12); pathologic expertise by Dr. Louis (Core C); assistance with vector engineering by Dr. Sena-Esteves; and MRI analysis by Dr. Weissleder. This project is designed to develop a strategy for reducing bulk in slow growing, benign tumors using vectors safe enough for eventual human use.